I thought you should never use triangles?
Almost undoubtedly the mesh would have been modeled using quads since it is better to work with. However, any mesh is actually converted to triangles at the lowest level for rendering. By ripping the model out of the game you are picking up the mesh in a form that has already been optimised for maximum efficiency in the game - ie, already converted to tris so the game engine does not have to deal with the more complicated quad-based geometry.